Debt - Narrative (Detail)			3 Months Ended		9 Months Ended
	Jan. 11, 2021 USD ($) day $ / shares Rate shares	May 04, 2020 USD ($) day $ / shares Rate	Sep. 30, 2021 USD ($) day Rate shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2021 USD ($) Rate shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2021 USD ($)	Sep. 30, 2021	Sep. 30, 2021 $ / shares	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Issuance of common stock, net					$ 12,110,000	$ 10,761,000
Ownership of convertible notes (as a percent)		25.00%
Proceeds from issuance of convertible debt, net of issuance costs					$ 334,410,000	$ 194,466,000
Debt instrument, weighted average interest rates								5.07%		4.91%
0.25% Convertible Senior Notes due 2028 | Convertible Debt
Line of Credit Facility [Line Items]
Stated interest rate (as a percent) | Rate	0.25%		0.25%		0.25%
Debt instrument, face amount	$ 345,000,000
Discount on principal amount (as a percent) | Rate	97.00%
Discount on shares	$ 10,600,000
Threshold trading days | day	20
Consecutive trading days | day	30
Conversion price on applicable trading day (as a percent)	130.00%
Convertible Notes, conversion ratio | Rate	1.51172%
Convertible Notes, conversion price (in dollars per share) | $ / shares	$ 66.15								$ 48.24
Dilutive effect of Convertible Notes (in shares) | shares			5,215,434		5,100,809
Redemption price of principal (as a percent)	100.00%
Ownership of convertible notes (as a percent)	25.00%
Interest expense, contractual coupon interest			$ 200,000		$ 600,000
Interest expense, accretion of debt discount			400,000		1,000,000
Interest expense, amortization of debt issuance costs			$ 8,400		$ 23,700
Effective interest rate on Convertible Notes (as a percent)					0.70%
0.25% Convertible Senior Notes due 2028 | Convertible Debt | Level 2
Line of Credit Facility [Line Items]
Estimated fair value of debt							$ 342,400,000
0.25% Convertible Senior Notes due 2028 | Convertible Debt | Debt Instrument, Redemption, Period One
Line of Credit Facility [Line Items]
Threshold trading days | day	20
Consecutive trading days | day	30
Conversion price on applicable trading day (as a percent)	130.00%
0.25% Convertible Senior Notes due 2028 | Convertible Debt | Debt Instrument, Redemption, Period Two
Line of Credit Facility [Line Items]
Threshold trading days | day	5
Consecutive trading days | day	5
Principal amount priced to investors (as a percent) | Rate	98.00%
1.25% Convertible Senior Notes due 2025
Line of Credit Facility [Line Items]
Dilutive effect of Convertible Notes (in shares) | shares			0	5,538,000	0	0
1.25% Convertible Senior Notes due 2025 | Convertible Debt
Line of Credit Facility [Line Items]
Stated interest rate (as a percent)		1.25%	1.25%		1.25%			1.25%
Debt instrument, face amount		$ 201,300,000
Discount on principal amount (as a percent) | Rate		97.00%
Discount on shares		$ 6,900,000
Threshold trading days | day		20
Consecutive trading days | day		30
Conversion price on applicable trading day (as a percent)		130.00%
Convertible Notes, conversion ratio | Rate		2.75198%
Convertible Notes, conversion price (in dollars per share) | $ / shares		$ 36.34							$ 48.24
Dilutive effect of Convertible Notes (in shares) | shares			5,538,360		5,538,360	3,112,801
Redemption price of principal (as a percent)		100.00%
Interest expense, contractual coupon interest			$ 600,000	$ 600,000	$ 1,900,000	$ 1,000,000
Interest expense, accretion of debt discount			300,000	1,800,000	900,000	2,700,000
Interest expense, amortization of debt issuance costs			$ 36,500	$ 25,600	$ 100,000	$ 44,700
Effective interest rate on Convertible Notes (as a percent)					1.96%
Convertible debt, if converted, value in excess of principal		$ 65,900,000
1.25% Convertible Senior Notes due 2025 | Convertible Debt | Level 2
Line of Credit Facility [Line Items]
Estimated fair value of debt							$ 280,300,000			$ 320,900,000
1.25% Convertible Senior Notes due 2025 | Convertible Debt | Debt Instrument, Redemption, Period One
Line of Credit Facility [Line Items]
Threshold trading days | day		20	20
Consecutive trading days | day		30	30
Conversion price on applicable trading day (as a percent)		130.00%	130.00%
1.25% Convertible Senior Notes due 2025 | Convertible Debt | Debt Instrument, Redemption, Period Two
Line of Credit Facility [Line Items]
Threshold trading days | day		5
Consecutive trading days | day		5
Principal amount priced to investors (as a percent) | Rate		98.00%
Over-Allotment Option
Line of Credit Facility [Line Items]
Issuance of common stock, net	$ 334,400,000	$ 194,500,000
Capped Call Transactions
Line of Credit Facility [Line Items]
Proceeds from issuance of convertible debt, net of issuance costs	$ 29,300,000
Capped call transaction, number of underlying shares | shares	5,200,000
Offering price per share (in dollars per share) | $ / shares	$ 85.75
Premium on offering price (as a percent)	75.00%
Public offering price (in dollars per share) | $ / shares	$ 49.00